In the semiconductor processing industry there are many instances where wafers are treated in thermal processors using a variety of gases, pressures and processing temperatures. The thermal processors are typically referred to as wafer processing furnaces, or more simply as furnaces. Most furnaces use a quartz processing vessel which encloses the process chamber. The process chambers are usually large enough for a significant number of wafers to be simultaneously processed. Wafer processing furnace arrays having capacities of 50-200 wafers are used. Furnace arrays are often in a vertical column arrangement wherein wafers are maintained in spaced parallel face-to-face relationship perpendicular to a vertical longitudinal axis.
Previously it has been the practice to load and unload wafers and substrates from such furnaces using a wafer handling robot or similar mechanical arm. Such robots or handling arms include wafer, substrates and panel engagement tools which are mounted at the distal ends of the arms. The wafer engagement tools are often devices called end effectors. These end effectors or other engagement tools engage and support each wafer as it is moved to and from the furnace array. Many end effectors utilize vacuum to hold the wafers.
Wafer processing furnaces typically have support rails which extend vertically within the processing vessel to support the wafers in spaced parallel relationship. The support rails typically have wafer support grooves or other wafer support features which receive the edges of the wafers to support them in their desired position. The wafer support features only engage a wafer along a narrow band adjacent the peripheral edge of the wafer.
The loading and unloading of wafer furnaces consumes significant time as each wafer is loaded or unloaded in turn. The processes of loading, unloading or otherwise moving such wafers to or from the furnaces are herein referred to as wafer transferring. Because of the close spacing of the adjacent wafers in a furnace array there must be precise mechanical maneuvering. Wafers are inserted parallel to the faces of the adjacent wafers with great care and exactitude. Each wafer is brought into position and then lowered axially a small distance and onto the support features of the furnace support rails. Conversely, when wafers are unloaded, the wafer transfer arm must very precisely insert the engagement tool beneath the wafer being unloaded. Misplacements can be catastrophic causing multiple wafers to be damaged or destroyed. Since each wafer can be of great value, any such mistakes can be very costly.
The care and precision needed to reliably load and unload wafers limits speed and further exacerbates the significant time needed to individually load and unload each wafer in a large wafer furnace array. The significance of the transfer times is further amplified because the processing furnaces are very costly pieces of production equipment which need to be fully utilized to provide more economic operation and reduced costs to the consumer.
Thus there is a need for improved transfer apparatus and methods which can reliably handle and transfer semiconductor wafers or other similar panels to and from processing equipment.